1. Field of the Invention
This application relates generally to nebulizers for use in analytical spectrometry such as inductively coupled mass spectrometry, and more specifically to direct injection nebulizers.
2. Description of the Related Art
Inductively coupled plasma atomic emission spectrometry (ICPAES) and ICP mass spectrometry (ICPMS) are practical techniques for trace and ultratrace elemental analysis. While many advances have been made in instrumentation, the introduction of a sample to the plasma represents the most problematic area, with liquid sample introduction being the most common. Many devices have been developed for aerosol generation and transport, each having its own benefits and limitations.
The pneumatic nebulizer-spray chamber arrangement is currently the primary sample introduction method for ICP spectrometry, mainly due to its simplicity and low cost. This arrangement presents, however, several drawbacks, namely low analyte transport efficiency (1–20%) and high sample consumption (1–2 mL/min), memory effects, spray chamber-induced interferences such as transient acid effects, and post-column broadening when coupled with chromatographic techniques for speciation analysis. These effects may be reduced through the use of micronebulizers and reduced-volume spray chambers integrated with− or without− the ICP torch. A simple, low-consumption, highly efficient nebulizer is often required in chromatographic applications and also for the direct analysis of semiconductor, biological, toxic, or forensic materials. In these and other cases, the sample is expensive, hazardous, or limited.
Two popular micronebulizers have been explored that eliminate the need for the spray chamber by directly introducing 100% of the sample into the plasma: the direct injection nebulizer (DIN) and the direct injection high efficiency nebulizer (DIHEN). Both devices offer fast response times, reduced memory effects, no transient acid effects, no solution waste and low sample consumption rates (1–100 μL/min) while exhibiting similar or improved detection limits, sensitivity and precision compared to conventional nebulizer-spray chamber arrangements. Although the DIN has an adjustable and exchangeable solution capillary, its versatility is limited due to its relatively complex setup, high costs, and requirement of a high-pressure pump for sample delivery. The DIHEN, however, is a simple concentric nebulizer that is less expensive compared to the DIN and does not require an additional high-pressure pump.
One weakness of the micronebulizers (including the DIN and DIHEN) in addition to their high cost is their greater susceptibility to nebulizer clogging compared to other types of nebulizers due to the smaller dimensions for the solution capillary and gas annulus areas. This limitation may destroy the nebulizer. In order to overcome the problem of clogging a large bore-DIHEN (LB-DIHEN) is used. Although nebulizer clogging is reduced for nebulization of slurries and solutions having a large amount of total dissolved solids, the performance of the LB-DIHEN is slightly worse than those of the DIHEN. Additionally, the close proximity of the nebulizer tip to the plasma increases the likelihood of accidental and gradual damage to direct injection nebulizers.
Accordingly, there is a need for a simple, low cost device that allows easy replacement of a solution capillary due to, for example, clogging or melting. In addition, the device should also allow for precise alignment of the capillary tip with respect to the nebulizer tip not only to improve nebulization, but also to increase the distance between the nebulizer tip and the plasma base, thereby protecting the nebulizer against melting